sticky in dec lx200ace

I have a lx200 14in. that binds and sticks when moving in dec.It`s rough and grabs at the start then runs fine.Once it restarts the problem re-appears. No problem in RA.I brought to the dealer in Montreal and he called the next day to say all was fine.Here`s the rub:it only does it in cold weather,say below 0deg cels.I set up a heat lamp in the observatory under the scope and after warming up it runs fine.BTW I`ve cleaned up the worm gear and ring and regreased withPete,s red grease but still no go.Any ideas..... thanks Walt